In time multiplexed telephone switching systems, it is necessary to constantly monitor the time slot integrity of data as it travels through the system to detect any cross connections between the time slots. These cross connections can occur from addressing faults when accessing data buffers (data buffer memory locations correspond to specific time slots in the data stream), which interface the port modules to the time multiplex switch (TMS). It is desirable to detect these time slot cross connect situations as soon as they occur, to allow the system to disconnect the faulty data path with a minimum of data errors.
One known system inserts successive bits of a pseudo-random binary sequence (PRS) into a dedicated bit position of successive time slots of data, prior to the data being stored into a data buffer. When the data from each time slot is retrieved, the contents of the dedicated bit position is compared against the expected binary value of the corresponding bit of the PRS. While this technique is fast, it requires dedicating one bit of each transmitted data word to provide the time slot integrity checking capability.